Jan. 18, 2011 -- Two new studies suggest the protein fragment beta-amyloid may be a useful biomarker to identify people at risk for Alzheimer's disease.

Researchers have long searched for such biomarkers to identify those at risk for Alzheimer's early in the course of the disease, before significant dementia occurs. That search has largely focused on beta-amyloid, which builds up in the brains of people with Alzheimer's.

A definitive diagnosis of Alzheimer's disease requires the presence of beta-amyloid deposits in the brain at autopsy.

The new studies suggest the protein may be a useful marker of disease long before death occurs.

Both studies appear Wednesday in TheJournal of the American Medical Association.

Highlighting Beta-Amyloid Deposits

In one study, researchers combined PET imaging with the experimental radioactive drug florbetapir, which is designed to highlight beta-amyloid deposits in the brain.

To prove its usefulness in living patients, the investigators designed a novel study involving people presumed to be in their last months of life due to either Alzheimer's or some other illness.

An average of 99 days before their deaths, 29 patients underwent PET imaging following intravenous administration of the experimental drug.

The imaging identified 15 patients who met the pathological criteria for Alzheimer's disease, and the diagnosis or lack of diagnosis was confirmed for all but one of the 29 patients at autopsy.

In a separate analysis involving 74 people between the ages of 18 and 50 with no evidence of cognitive decline, all of the images were negative for significant beta-amyloid deposits.

Study researcher Christopher Clark, MD, says the finding shows the value of the imaging technique for ruling out Alzheimer's disease in patients with memory loss and other symptoms of cognitive decline.

Clark is medical director for Avid Radiopharmaceuticals, which developed florbetapir. Avid was purchased by drug maker Eli Lilly & Company late last year.

"This study shows a very high correlation between the imaging and the presence of amyloid in the brain at autopsy," he tells WebMD.

FDA Advisory Panel

Lilly is seeking FDA approval to market florbetapir for the detection of beta-amyloid in the brain, and an FDA advisory panel is scheduled to discuss the matter on Thursday.

But preliminary materials released by FDA today raised doubts about the drug's chances for approval.

In a briefing posted on the FDA's web site in preparation for the meeting, at least one reviewer concluded that data from the study failed to provide convincing evidence to support the drug's usefulness. The reviewer cited "significant limitations" in the study's design, size, and execution that "cast doubt on the ... validity, reproducibility, and clinical utility" of the imaging procedure."

A spokesperson for Eli Lilly declined to comment on the briefing Tuesday, telling WebMD the company was "looking forward" to making its case for the drug at Thursday's meeting.

Beta-Amyloid in the Blood

In the second study, researchers reported that low levels of beta-amyloid in the blood predicted cognitive decline over a nine-year period.

The study included close to 1,000 older adults enrolled in a larger health study with no evidence of dementia at enrollment.

Beta-amyloid levels were measured soon after enrollment and the participants were followed for close to a decade.

Low levels of amyloid 42/40 at enrollment were found to be associated with greater cognitive decline, especially among less educated people and those with lower reading skills.

This finding bolsters the hypothesis that people with greater cognitive reserves, as measured by higher education and higher literacy, may be less likely to develop dementia than those with fewer reserves when beta-amyloid is present in the brain.

"Cognitive reserve is a broad concept used to explain why some individuals have measurable pathological burden of beta-amyloid (at autopsy) but do not experience clinical symptoms of cognitive decline," they write.

Seeking Answers

Alzheimer's researcher Monique Breteler, MD, PhD, tells WebMD that both the blood and imaging approaches show promise, but she says their usefulness at present may be limited to research.

Breteler is a professor of epidemiology at Erasmus University in the Netherlands.

"We don't have good treatments for Alzheimer's disease, and all the evidence suggests that when we find these treatments they will be most effective early in the course of disease," she says.

In an editorial also published in The Journal of the American Medical Association, Breteler concluded that more rigorously designed studies are needed to confirm the clinical usefulness of the techniques.

"The stakes involved in finding good biomarkers for Alzheimer's disease and other neurodegenerative diseases are high indeed -- too high to be able to afford jumping to unwarranted conclusions and heading in the wrong direction," she writes.